Currently, the most widely used method for detecting growth in children is to measure changes in the total height of the child over selected periods of time. Preferably, such measurements should be made as frequently as possible (i.e. at least once every three months), in order to determine whether the treatment prescribed for a child having a particular disorder is enhancing or inhibiting growth or to determine the course of normal growth and development in a child.
A major shortcoming of measuring the total height of the child to detect growth is that serious errors can be introduced in the measurement. For example, variations in spine compression and head posture will contribute to incorrect assessments of actual growth. Consequently, the recommended therapy, based on such measurements, can be inappropriate.
Recognizing this shortcoming of detecting growth by measuring total height, a method and apparatus has been suggested and put into actual use, whereby measurements of the length of the lower leg, are used as a measure of growth. Growth, 1983, 47, 53-66 describes this method and apparatus.
By restricting the measurement of growth to the lower leg, most of the major sources of errors in the measurements of overall height are eliminated entirely. Such measurements have much less relative error than measurement of total body stature which, as indicated above, includes additional variations, for example, in spine compression and head posture. Hence it is possible to reduce the measurement error to such an extent that accurate assessments of growth can be made as frequently as once a month. This can result in a substantial reduction in the cost of various therapies and can assure greater success for the clinical outcome.
The method and apparatus described in the aforementioned article, however, suffers from a major shortcoming which affects the accuracy of the measurements of growth in the lower leg. Typically, the measure of lower leg growth is derived from the average of a number of length measurements made in one measurement session In the method and apparatus described in the aforementioned article, the components which engage the leg and from which the length measurements are made are set to measure directly to the highest attainable height of the knee of the patient. Each such measurement necessarily includes the body tissue above the knee and beneath the heel of the patient. With the top of the knee and the bottom of the foot as the end points of the length measurements, the effects of body tissue above the knee and beneath the heel can introduce errors in the measurements due to variations in the compression of the body tissue from one measurement to the next. The individual conducting the measurements does not know the degree of compression of the body tissue required to duplicate conditions from one measurement to the next. As a result, length measurements subsequent to the first one are biased by looking for the same highest measurement as the first measurement because of a reluctance to rely on the "feel" of the components which engage the endpoints of the leg. To the extent that the individual conducting the length measurements is willing to rely on "feel" to duplicate body tissue compression conditions from one length measurement to the next, accuracy becomes a real concern because of the difficulty in compressing body tissue the same amounts based on the "feel" of the measurer.